Microevolutionary Events Involving Narrow Host Plasmids Influences Local Fixation of Vancomycin-Resistance in Enterococcus PopulationsReportar como inadecuado

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Vancomycin-resistance in enterococci VRE is associated with isolates within ST18, ST17, ST78 Enterococcus faecium Efm and ST6 Enterococcus faecalis Efs human adapted lineages. Despite of its global spread, vancomycin resistance rates in enterococcal populations greatly vary temporally and geographically. Portugal is one of the European countries where Tn1546 vanA is consistently found in a variety of environments. A comprehensive multi-hierarchical analysis of VRE isolates 75 Efm and 29 Efs from Portuguese hospitals and aquatic surroundings 1996–2008 was performed to clarify the local dynamics of VRE. Clonal relatedness was established by PFGE and MLST while plasmid characterization comprised the analysis of known relaxases, rep initiator proteins and toxin-antitoxin systems TA by PCR-based typing schemes, RFLP comparison, hybridization and sequencing. Tn1546 variants were characterized by PCR overlapping-sequencing. Intra- and inter-hospital dissemination of Efm ST18, ST132 and ST280 and Efs ST6 clones, carrying rolling-circle pEFNP1-pRI1 and theta-replicating pCIZ2-like, Inc18, pHTβ-like, two pRUM-variants, pLG1-like, and pheromone-responsive plasmids was documented. Tn1546 variants, mostly containing ISEf1 or IS1216, were located on plasmids 30–150 kb with a high degree of mosaicism and heterogeneous RFLP patterns that seem to have resulted from the interplay between broad host Inc18 plasmids pIP501, pRE25, pEF1, and narrow host RepA N plasmids pRUM, pAD1-like. TAs of Inc18 ω-ε-ζ and pRUM Axe-Txe plasmids were infrequently detected. Some plasmid chimeras were persistently recovered over years from different clonal lineages. This work represents the first multi-hierarchical analysis of VRE, revealing a frequent recombinatorial diversification of a limited number of interacting clonal backgrounds, plasmids and transposons at local scale. These interactions provide a continuous process of parapatric clonalization driving a full exploration of the local adaptive landscape, which might assure long-term maintenance of resistant clones and eventually fixation of Tn1546 in particular geographic areas.

Autor: Ana R. Freitas, Carla Novais, Ana P. Tedim, María Victoria Francia, Fernando Baquero, Luísa Peixe, Teresa M. Coque

Fuente: http://plos.srce.hr/


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